NTSC / PAL ... ?

Essential Differences.

There are quite a lot of technical differences between NTSC and PAL video signals, but on the basis that you probably don’t want to be a TV engineer we’ll ignore them all except for these two:-

FRAME RATE – NTSC uses 60Hz (that is 60 fields a second, equal to 30 frames per second) and PAL uses 50Hz (yes you’ve guessed it 50 fields a second equal to 25 frames per second).

COLOUR FREQUENCY – This is the part of the video signal that carries the information about the colour. All that really matters is that American NTSC uses a different colour frequency compared to PAL.

NTSC uses 3.58MHz

PAL uses 4.43Mhz

LINE RATE

PAL has 625 lines per frame while the American NTSC has 525

To view NTSC material

a) With a DVD player

Assuming that your DVD player is able to accept an NTSC disc (we’re going to ignore region coding issues here.) then just connect the output to your TV and see what happens.

On some DVD's there is a sub menu under setup or something similar and you can often force the output to be always PAL, always NTSC or switch automatically  to match the disc type.

If you can force the output to PAL then you would in theory at least be able to watch and record that signal. usually however because of copy inhibit measures you can only watch the output

b) With a VCR

Some PAL VCR’s are NTSC playback compatible and some aren’t. If you’re not sure then try it and see what happens. NTSC tape speed is different to PAL so playing an NTSC tape on a non-compatible VCR will produce a horrible mess of a picture, and the audio will sound speeded up. If your VCR won’t play the tape properly then you have four solutions to viewing your NTSC tape, all of which involve parting with money:-

1)     Buy an NTSC compatible VCR – obvious but effective

2)     Buy a true multi-standard VCR – expensive but very useful in the long term.

3)     Import an NTSC VCR – cheap to begin with, but you’ll also need a mains voltage converter and it won’t be a deal of use for taping Eastenders (different tuner..)

4)     Send your tape to a duplicating house and ask them to copy it onto PAL VHS - by far the cheapest solution – especially if the tape is a one-off and you’re unlikely to get any more.

Assuming you can get the tape to play in the VCR your troubles aren’t necessarily over as it probably will not be giving a true NTSC signal. Sometimes they can just play the tape but give out an NTSC signal. Alternatively some will produce a “quasi-PAL” signal in which the colour frequency is altered but not the frame rate. This is OK if your TV can cope, but its not much use otherwise. In fact it can be a hindrance as some signal converters expect to see a nice pure true NTSC signal coming in before they’ll do their job properly.

Quasi PAL signals make use of the fact that modern TVs are capable of locking to either 50 or 60 Hz signals. The NTSC signal is sent to the TV still as a 60Hz signal but with the colour (or should that be color for NTSC) frequency changed from the 3.58Mhz of NTSC to 4.43MHz of PAL, so you get a picture you can watch, but your VCR can't record.

Once you’ve got playback sorted then usually one of the following will happen:-

1) You get a nice clean stable colour picture. Great! – you have an NTSC compatible TV and can watch your NTSC DVD’s without any problems.

2) You see a nice stable picture but only in black and white

This happens because your TV is able to lock onto a 60Hz NTSC signal but your  TV cannot compensate for the difference in colour frequency. The solution is to use an analogue NTSC to Pal signal convertor which changes the colour frequency back to where the PAL TV expects it to be. (Quasi PAL) There are many on the market, Keene Electronics can supply one 

3) You see a horrible jumbled mess on screen. This happens when the TV isn’t able to lock onto a 60Hz signal. The solution is to use a digital NTSC to Pal convertor to change the signal into something the TV can recognise.

Recording NTSC material (onto PAL VHS)

(Assuming you know that this may well be illegal)

PAL VCR’s have to receive the signal at 25 frames per second. NTSC signals (and NTSC signals routed through an analogue convertor) are 30 frames per second. If you try to record it you get a horrible picture which rolls all the time (looking like the tracking has gone haywire). The only solution is to use a digital NTSC to PAL convertor. These are much more expensive than the analogue converters because as they contain enough memory to read the signal in at 30 fps and read it out again at 25 fps. Since you’re effectively ditching 5 frames per second the output will look very slightly jerky when compared to the source, but this is only usually noticeable on fast pans etc.  Digital converters come with different amounts of memory to perform the conversion, the cheapest use 2MB, which gives around 200 lines resolution – OK for a quick VHS “backup” but a bit limited for large screen viewing. 4MB versions will give better resolution (around 300 lines) and 8MB are the money-no-object option.

Key differences;

NTSC is 30fps PAL is 25fps

Most TV’s are happy with either fps but VCR’s (usually) will only be stable with 25fps.

NTSC has a different colour frequency to PAL

3.58MHz for NTSC 

4.43MHz for PAL

Some TV’s can cope with either frequency – some can’t. (you just get a B&W picture)

Analogue converters change the colour information only – to restore the colour if you get a stable B&W picture). Digital converters change both colour information and the frame and line rates, allowing viewing on any TV plus recording on a PAL VCR.

The sync frequencies for PAL are 

Vertical is 50 (50 fields or 25 frames per second in an interlaced signal)

Horizontal is 15,625 Hz for an interlaced picture and 31,250 for a non-interlaced picture.

The sync frequencies for NTSC are 

Vertical is 60 (60 fields or 30 frames per second in an interlaced signal)

Horizontal is 15,750 Hz for an interlaced picture and 31,500 for a non-interlaced picture.